The invention relates to a composite panel from which an internal bathtub casing can be manufactured by deep drawing, whereby a coating of poly(methyl methacrylate) (PMMA, acrylic glass) is placed on a substrate of acrylonitrile-butadiene-styrene (ABS) in particular.
EP-A-0 225 500 discloses an option for fabricating internal bathtub casings, the quality of which is approximately equivalent to that of poured acrylic glass, by appropriate selection of the melt index of an acrylic layer coextruded with a substrate made of ABS. A measure of the quality of the insert in this case is the number of filling cycles with hot and cold water that the bathtub can be subjected to according to the relevant CEN specifications until the first fine hairline cracks are perceptible. In this type of test, the bathtub is filled alternately with hot water of 95.degree. C. and cold water of 12.degree. C., whereby the test conditions are precisely specified.